08 January 2025
Digestate, a by-product of anaerobic digestion, is increasingly popular as a sustainable fertiliser. However, many myths and misunderstandings surround its use. Let’s separate fact from fiction.
1. Digestate can totally replace fossil fuel fertilisers – False
While digestate provides ample phosphorus (P) and potassium (K), it may require nitrogen supplementation for certain crops and soil conditions. It also contains many micronutrients such as sulphur, magnesium, and selenium. Its suitability depends on the crop and existing soil nutrient levels.
2. Digestate is expensive and difficult to spread – True and False
When used locally, digestate is cost-effective, particularly when spread using an umbilical cord system, which can cost as little as £2.50 per tonne to spread. Tractor-and-tanker methods are pricier but still economically viable, given digestate's fertiliser value.
3. Spreading digestate causes damage to the fields through compaction – True and False
If heavy tractors and tankers spread digestate on wet fields, compaction can occur. However, umbilical cord systems reduce land pressure and mitigate this risk. Proper timing and spreading techniques are key to avoiding compaction.
4. Digestate damages watercourses when spread – True and False
If spread on frozen land, very wet fields, or land adjacent to watercourses, digestate can leach into waterways. However, appropriate storage and application practices prevent this, ensuring nutrients are absorbed by crops instead of polluting watercourses.
5. Digestate is odourless – False
Digestate emits a mild ammonia odour when spread, though it dissipates quickly. Compared to traditional organic fertilisers like pig or chicken manure, digestate has significantly lower odour emissions.
6. Digestate kills worms and other insects – True and False
When applied correctly, digestate supports soil health, benefiting worms and insects. Over-application, however, can harm soil ecosystems.
7. Digestate comes in liquid and solid forms – True
Digestate can be whole, liquid, or fibre-based solid. Each format has advantages and disadvantages, but all effectively recycle organic nutrients into the soil.
8. Digestate loses its fertiliser value when stored – True and False
Uncovered digestate loses nitrogen to the air over time, reducing its fertiliser value. However, phosphorus and potassium levels remain stable. Covered storage, therefore, helps maintain its fertiliser value for longer by retaining nitrogen.
Digestate is a versatile and sustainable fertiliser, but it requires proper use and understanding. By adopting best practices, farmers can maximise its benefits while minimising potential drawbacks.